High-frequency transmission line or cable and connector therefor



Dec. 6, 1949 Eh C. CORK 2,490,622

HIGH-FREQUENCY TRANSMISSION LINE OR CABLE AND CONNECTOR THEREFOR FiledMay l5, 1945 Patented Dec. 6, 1949 HIGH-FREQUENCY TRANSMISSION LINE ORCABLE AND CONNECTOR THEREFOR Edward Cecil Cork, Ealing, London, England,as-

signor to Electric & Musical Industries Limited, Hayes, Middlesex,England, a company of Great Britain Application May 15, 1943, Serial No.487,166 En Great Britain `anuary 15, 1941 Section 1, Public Law .690,August 8, 1946 Patent expires January 15, 1961 8 Claims.

rihis invention relates to high frequency transmission lines orapparatus and connectors therefor.

High frequency transmission lines are usually in the form of cablescomprising an outer tubular conductor and an inner conductor disposedcentrally within the outer conductor, such form of cable being usuallyreferred to as of the concentric type. It is customary to connect twolengths of such cable together or to connect a portion of a cable tohigh frequency apparatus or to connect two pieces of high frequencyapparatus together by means of various types of connectors. The termconnector herein employed is intended to cover a device comprisingessentially two separable parts, each part comprising an inner conductorand an outer conductor insulated therefrom, whereby each part can beconnected to a transmission line of the concentric type so as to form acontinuation both of the inner and outer conductors of said line, thetwo parts being arranged to be separated as by the provision of plug andsocket portions, bayonet connecting portions, screw-threaded portions orthe like which permit disconnection without the necessity ofdisconnecting the line from either part of the connector, the two partsof the connector when in engagement with one another serving to connectelectrically the inner and outer conductors of one line to the inner andouter conductors respectively of the other line. The term connector alsoincludes constructions in which the outer conductor of one or both partsof the connector is flanged for connection to the screening box of highfrequency apparatus.

When the transmission lines or cables or the apparatus are designed foroperating on wavelengths of a few centimetres it is found that theconnectors introduce irregularities due to the inductance and/orcapacity of the connectors which become of increasing effect as thewavelength of the energy it is desired to transmit becomes smaller. Atsuch centimetre wavelengths the connector must be considered as forminga Y 'the result that reflection occurs of the high frequency energypassing through the connectors.

One of the objects of the present invention is to overcome or reducethese diiiculties.

According to one feature of the invention, a high frequency transmissionline or apparatus is coupled to another line or apparatus having asimilar characteristic impedance by means of a connector which is ofsuch a length and has such a characteristic impedance that the connectorsubstantialiy matches the impedances of the coupled elements, wherebyhigh frequency energy can be transmitted through said connectorsubstantially without reflection.

When reference is made herein to a high freq ency transmission line orapparatus this means a transmission line or apparatus arranged totransmit energy of a wavelength up to 50 centimetres. The term highfrequency energy means energy of a like wavelength.

According to another feature of the invention, a high frequencytransmission line or apparatus is coupled to another line or apparatushaving a similar characteristic impedance by means of a connector whichpreferably has a similar characteristic impedance and the length ofwhich is equal or approximately equal to a half wavelength or to anintegral multiple of half-wavelengths of the high frequency energytransmitted between said coupled elements, whereby said energy can betransmitted through said connector substantially without reflection.

In some cases it is desired to connect a high frequency transmissionline or apparatus to another transmission line or apparatus havingcharacteristic impedances which are not matched. In order to preventreflection occurring due to mismatch it is the practice to insertbetween the elements to be coupled an impedance transforming devicewhich at high frequencies is usually Ain the form of a transmissionline.

According to another feature of the present invention, a high frequencytransmission line or apparatus is coupled to another line or apparatushaving a dissimilar characteristic impedance by means of a connectorwhich has such a length and such a characteristic impedance that theconnector acts as an impedance transformer whereby high frequency energycan be transmitted between said coupled elements substantially withoutreflection.

If desired, the connector may be provided with an adjustable element orelements arranged to afford a shunt or series loading impedance. Thishas the advantage that the electrical length of the connector need notbe accurately determined since by adjusting the adjustable element thede- 3 sired electrical length or impedance can be imparted to theconnector.

In the specification of United States Patent No. 2,270,416 issuedJanuary 20, 1942, to Edward Cecil Cork, there are disclosed variousforms of filters in which the resistance, inductance and capacity of thefilter can be introduced in the form of sections of transmission lines.

According to another feature of the invention one or both parts of saidconnector is or are provided with an additional portion or portions oftransmission line which is or are so associated with said part or partsthat the connector acts as a lter for some lcomponents of the highfrequency energy transmitted between the coupled elements.

According to another feature of the invention there is provided aconnector for coupling together high frequency transmission lines orapparatus having similar characteristic impedances, said connectorhaving a substantially uniform impedance throughout its length thusavoiding` lumped impedances along its length and the connector is suchthat if high frequency energy is transmitted therethrough of awavelength such that the connector is a half wavelength long or amultiple of nali wavelengths long, said energy will be transmittedsubstantially without redection.

According to another feature of the invention there is provided aconnector for coupling together high frequency transmission lines orapparatus having dissimilar characteristic impedances, said connectorhaving a substantially uniform impedance along its length and has such acharacteristic impedance that if high frequency energy is transmittedtherethrough which is of a wavelength such that the connector is aquarter wavelength long or an odd integral multiple of quarterwavelengths and if said energy is transmitted via said connector fromtransmission lines or apparatus having such dissimilar characteristicimpedance that the characteristic impedance of said connector is thegeometric means of the impedance of said lines or apparatus, said energywill be transmitted substantially without reflection. Preferably thespace between the inner and outer conductors of the elements of theconhector is filled with insulating material, the insulating materialemployed, of course, being taken into consideration in determining theelectrical length of the connector as distinct from its physical length.

In this specification where reference is made to the length of theconnector this means the electrical length as distinct from its physicallength, unless the context implies otherwise.

In order that the features of the invention may be clearly understoodandv readily carried into effect, they will now be described withreference to the accompanying drawings, in which:

Figure l illustrates a longitudinal section of one form of connectorVdesigned for use with transmission lines or apparatus having eithersimilar impedance or dissimilar characteristic impedances, and

Figure 2 illustrates a longitudinal section of a connector designed tooperate as a lter.

Referring now to Figure 1 of the drawing, the connector shown is of theplug and socket type comprising two parts 3 and 4 which are shownseparated, each part comprising an outer tubular conductor 5 and 6 andan inner conductor 1 and S, the outer conductor 5 having a reducedportion 9 arranged as a sliding fit within the internally reducedportion i0 of the outer conductor 6, the inner conductor l beingprovided with a bore il whilst the inner conductor t is provided with aplug portion i2. The two parts of the connector are arranged to beplugged together in the well known manner so that the outer conductors 5and 6 and the inner conductors l and 8 are electrically connectedtogether respectively. The space between the outer conductor 5 and theinner conductor 'i is filled with insulating material i3, whilst thespace between the outer conductor f5 and the inner conductor is alsopartially lled with insulating material i4, the arrangement being suchthat when the two portions are plugged together the whole space betweenthe inner and outer conductors is filled with insulating material. Inorder to connect the outer conductor of a concentric line to the outerconductors 5 Vand and the inner conductor of the line to the innerconductors 'l and 8, any suitable clamping means may be provided forthis purpose. In most cases the inner conductor of the line will besoldered to the inner conductors of the connector whilst the outerconductor of the line may be clamped to the outer conductors of theconnector by a screw-threaded clamping device. The insulating materiali3 and le may be of any suitable form such as that shown by the tradename Polythene, this material being a polymer of ethylene.

Where the device shown in Figure l is intended to couple together twoelements such as a cable or high frequency apparatus having similarcharacteristic impedances, the lengthof the conductor should beapproximately equal to a half wavelength of the high frequency energytransmitted along the cable or by the apparatus or an integral multipleof half wavelength. It is preferred that the characteristic impedance oithe connector should also be equal to the characteristic impedance ofthe elements to be coupled, it being readily possible to impart thedesired impedance to the connector, taking into consideration itsphysical dimensions and the di-l electric constant of the insulatingmaterial employed in its construction.

It is preferred that the impedance of the conhector should be uniformthroughout its length so as to avoid as far as possible .theintroduction of lumped impedances at points along the length of theconnector. This can be achieved with the construction shown in Figure lby lling the space between the inner and outer connectors with theinsulating material and by avoiding the introduction of metal partswhich have dimensions greatly diifering from one another in the twoparts of the connector. Thus by employing a connector in this mannerhigh frequency energy can be transmitted between the elements coupled bysaid connector without substantial reection.

Where the connector shown in Figure 1 is intended to be employed as animpedance matching transformer, its length should be equa-l orapproximately equal to a quarter wavelength or to an odd integralmultiple of quarter wavelengths of the high frequency energytransmitted. The characteristic impedance of the connector in this caseshould be chosen to be equal to the geometric mean of the impedances tobe matched as to produce the required transformation ratio, thus againpermitting the transmission of high frequency energy substantiallywithout reflection.

If desired the lengths of the connectors need not be accurately madeequal to a half or quarter Wavelength Qr their equivalents, as the casemay be, but may be made approximately equal thereto and the desiredelectrical length and impedance can be imparted toI the connector byproviding an adjustable element or elements so as to afford either aseries or a shunt loading impedance, as suggested in the specication ofBritish Patent No. 489,704. ThusV the length of the connector may besuchas to afford a partial impedance match and a loading impedance isprovided to eiect an accurate match. The loading impedance may take theterm of an adjusting screw I 5, which is threaded. intoa part of theAconnector at right angles thereto so as effectivelyto provide a shuntloading impedance or a screw threaded sleeve I6 may be provided,surrounding the outer conductor 6 and arranged so that it can be causedto engage, forexample, an abutment in the part 3 so that instead of thetwo parts when plugged together being` disposed with the insulatingmaterial I3 and I4 abutting, a space is left so. as to constitute aseries loading impedance.

Figure 2 of the drawings illustrates a connector which is providedy withadditional portions or" transmission line so that the connector canrunen tion as a lter. A wide variety of iilters can be constructed inaccordance with this feature of the invention, and in the example showneach part 3 and 4 of the connector is provided with a lateral extensionin the form-f a portion o a transmission line, which in some cases maybe a quarter of a wavelength long, the two portions being indicated bythe reference numerals I and I8. The outer conductors ofthe portions Ii'and I8 are directly connected to the outer conductors 5 and 8respectively of the parts 3A and 4, whilst the inner conductors I 8 and2B of the portions I! and I8 may be coupled to the inner conductors Tandy 8. Capacity coupling is shown in the ngure, but othercoupling'means may be used ifY desired. This capacity coupling isaiTOrded in the example shown by disposing the ends of the innerconductors I9 and 2li in proximity to the inner conductors 'I and 8, andin some cases this capacity coupling can be increased by enlarging thediamn eter of the inner conductors I and 8 as. indicated at 2l and 22and byy providing the ends of the conductors Irland' 29 with plates 23and 2t. The spaces between the outer and inner conductors of theportions I'!V and I8 are also preferably filled with insulatingmaterial. The length of transmission line between the portions I'l andI3 will dependA on the type and design of the nlter. The length of theconductor can, however, be such as to constitute a matchingimpedance ora transformer, as described above.

What I claim is:

1. A connector for connecting together high frequency transmission linesincluding a pair of separable parts, each part including at least a pairof electrically conductive members maintained in position relative toone another by solid insulating means, each ofl the electricallyconductive members ofV one part having a correspond-- ing member in theAother part, and arranged for telescopic engagement with thecorresponding member in said other part, saidsolid insulating meansbeing so arranged` that when said parts are in engagement the spacebetween said conductive members is substantially entirely filled bysolid insulating means, said connector having an electrical length, whensaid parts are in engagement, substantially equal to an integral multiple of one-quarter wavelength, the spacing between said conductivemembers and their dimensions being so related to the length of saidconnector that energyy Qn one of said transmission lines is transferredvtothe other ofvsaid transmis sion lines without reflection, theconductive members of said parts beingv so arranged that the spacing anddimensionsl or said members. isy uni form over their entire length whensaid parts are in engagement.

2. A connector for connecting together high frequency transmission linesof similar characteristic impedance, including; a pair of separableparts, each part includingA at least, a pair of electrically conductivemembers,l maintained in position relative to one another'by solidinsulating means, each of the electrically conductive members of onepart having al corresponding member in the other part and arranged fortelescopic engagement with the corresponding member in said other part,said solid insulating meansbeing so arranged that when said parts are inengagement the space between said conductive members is substantiallyentirely lled by solid insulating means, said connector having anelectrical length, when said parts are in engagement, sub.- stantiallyequal to the integral multiple ofi one-r half wavelength, the spacingbetween said conductive members and their dimensions being so related asto not greatly differ in the twoy parts of said connector.

3. A connector for connecting together high frequency transmission linesincluding a pair of separable parts, each partv including at least apair of electrically conductive members'maintained in position relativeto` one another by solid insulating means, each of theelectrically'conductive members of one part having a correspondingmember in the other part, and arranged for telescopic engagement withthe corresponding memloer in said other part, said solid insulatingmeans being so arranged that when said parts are in engagement the spacebetween said conductive members is substantially entirely iilled. bysolid insulating means, said connector having an electrical length, whensaid parts are in engagement, substantially equal to an integralmultipleof one-half wavelength, the spacing between said conductive members andtheirv dimensions being so related that the characteristic impedance ofsaid connector is equal to that of: saidj lines whereby energy on one ofsaid.. transmission. lines is transferred to the other ofV said.transmission lines without reiiection, the conductive members of saidparts being so arranged. that the spacing and dimensions of said membersis uniform over their entire length when saidv parts are: in engagement.

4. A connector for connecting together high frequency transmission linesincluding a pair of separable parts, each part including atleast a pairof electrically conductivev members maintained in position relative toone another by solid insulating means, each of the electricallyconductive members of one part having a corresponding member in theother part, and adapted to engage the corresponding member in said otherpart, said solid insulating means being so arranged that when said partsare-in engagement the space between said conductive members issubstantially entirely lled by solid insulating means, and arranged fortelescopic engagement with the corresponding member in said other part,said connector having an electrical length, when said parts are inengagement, substantially equal to an integral multiple of one-halfwavelength, the spacing between said conductive members and theirdimensions being so related that the characteristic impedance oi saidconnector is equal to that of said lines whereby energy on one of saidtransmission lines is transferred to the other of said transmissionlines without reflection, one of said pair of electrically conductivemembers being in the form of a tubular sheath concentrically arrangedabout another of said members as an inner conductor, the conductivemembers of said parts being so arranged that the spacing and dimensionsof said members is uniform over their entire length when said parts arein engagement.

5. A connector for connecting together high frequency transmission linesof dissimilar characteristic impedance, including a pair of separableparts, each part including at least a pair of electrically conductivemembers maintained in position relative to one another by a solidinsulating means, each of the electrically conductive members of onepart having a corresponding member in the other part and arranged fortelescopic engagement with the corresponding member in said other part,said solid insulating means being so aranged that when said parts are inengagement the space between said conductive members is substantiallyentirely filled by solid insulating means, said connector having anelectrical length when said parts are in engagement substantially equalto an odd multiple of one-quarter wavelength, the spacing between saidconductive members and their dimensions being so related as to notgreatly differ in the two parts of said connector, and further sorelated to the length of said connector that energy on one of saidtransmission lines is transferred to the other` of said transmissionlines without reflection.

6. A connector for connecting together high frequency transmission linesof dissimilar characteristic impedance, including a pair of separableparts, each part including at least a pair of electrically conductivemembers maintained in position relative to one another by a solidinsulating means, each of the electrically conductive members of onepart having a corresponding member in the other part and arranged fortelescopic engagement with the corresponding member in said other part,said solid insulating means being so arranged that when said parts arein engagement the space between said conductive members is substantiallyentirely filled by solid insulating means, said connector having anelectrical length when said parts are in engagement substantially equalto an odd multiple of one-quarter wavelength, then spacing between saidconductive members and their dimensions being so related as to notgreatly diier in the two parts of said connector, and further so relatedto the length of said connector that energy on one of said transmissionlines is transferred to the other of said transmission lines withoutreiiection, one of said pair of electrically conductive members being inthe form of a tubular sheath concentrically arranged about another ofsaid members as an inner conductor.

7. A connector for connecting together high frequency transmission linesof similar characteristic impedance, including a pair of separableparts, each part including at least a pair of electrically conductivemembers maintained in position relative to one another by solidinsulating means, each of the electrically conductive members of onepart having a corresponding member in said other part, and adapted fortelescopic engagement with the corresponding member in said other part,said connector having an electrical length, when said parts are inengagement, substantially equal to an integral multiple oi onequarter ofa Wavelength, said solid insulating means being so arranged that whensaid parts are in engagement the space between said conductive membersis substantially entirely filled by solid insulating means, the spacingbetween said conductive members and their dimensions being so related asto not greatly diier in the two parts of said connector, and anadjustable shunt loading impedance connected between said conductivemembers near one end of at least one of said parts.

8. A connector for connecting together high frequency transmission linesof similar characteristic impedance, including a pair oi separableparts, each part including at least a pair of electrically conductivemembers maintained in position relative to one another by solidinsulating means, each of the electrically conductive members of onepart having a corresponding member in the other part and arranged fortelescopic engagement with the corresponding member in said other part,said solid insulating means being so arranged that when said parts arein engagement the space between said conductive members is substantiallyentirely filled by solid insulating' means, said connector having anelectrical length, when said parts are in engagement, substantiallyequal to an integral muitiple of one-half wavelength, the spacingbetween said conductive members and their dimensions being so related asto not greatly differ in the two parts of said connector, and anadjustable shunt loading impedance connected between said conductivemembers near one end of at least one ci said parts, said impedanceincluding a screw threaded member in engagement with one of saidconductive members and in adjustable capacitive coupling relation withanother of said members.

EDWARD CECIL CORK.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 2,207,690 Cork et al July 9, 19402,233,166 Hahn Feb. 25, 1941 2,241,582v Buschbeck et al May 13, 19412,267,371 Buschbeck Dec. 23, 1941 2,332,952 Tischer et al Oct. 26, 19432,401,344 Espley June 4, 1946 2,402,540 Espley June 25, 1946 FOREIGNPATENTS Number Country Date 488,254 Great Britain June 23, 1938

